Method for cooling a direct injection pump

ABSTRACT

Methods and systems are provided for cooling a high pressure fuel pump. One method includes, when a spill valve is in a pass-through state, circulating fuel from a compression chamber of the high pressure fuel pump to a step room of the high pressure fuel pump. The fuel circulation through the step room may provide for a reduction in fuel temperature in the step room, and thus, the high pressure fuel pump.

FIELD

The present application relates generally to cooling a direct injectionfuel pump in fuel systems in internal combustion engines.

SUMMARY/BACKGROUND

Port fuel direct injection (PFDI) engines include both port injectionand direct injection of fuel and may advantageously utilize eachinjection mode. For example, at higher engine loads, fuel may beinjected into the engine using direct fuel injection for improved engineperformance (e.g., by increasing available torque and fuel economy). Atlower engine loads and during engine starting, fuel may be injected intothe engine using port fuel injection to provide improved fuelvaporization for enhanced mixing and to reduce engine emissions.Further, port fuel injection may provide an improvement in fuel economyover direct injection at lower engine loads. Further still, noise,vibration, and harshness (NVH) may be reduced when operating with portinjection of fuel. In addition, both port injectors and direct injectorsmay be operated together under some conditions to leverage advantages ofboth types of fuel delivery or in some instances, differing fuels.

In PFDI engines, a lift pump (also termed, low pressure pump) suppliesfuel from a fuel tank to both port fuel injectors and a direct injectionfuel pump (also termed, a high pressure pump). The direct injection fuelpump may supply fuel at a higher pressure to direct injectors. Duringoperation, one or more hot spots may be formed on a bottom surface of apump piston within the direct injection fuel pump. As such, fuel may beexposed to the bottom surface of the pump piston when residing within orflowing through a chamber (herein termed a step room) formed underneaththe bottom surface of the pump piston. Accordingly, fuel may be heatedleading to fuel vaporization within the step room. Further, theevaporation of fuel may overheat the step room and may increase alikelihood of the pump piston seizing within a bore of the directinjection fuel pump.

An example approach shown by Marriott et al. in US 2013/0118449 enablescooling of the step chamber via fuel circulation. Herein, fuel from alow pressure fuel supply line is circulated to the step room of thedirect injection fuel pump and thereupon returned to the low pressurefuel supply line upstream of an accumulator. Further, the flow of fuelthrough the step room is primarily driven by a change in volume of thestep room due to pump piston motion.

The inventors herein have recognized a potential issue with the exampleapproach of Marriott et al. For example, a direct injection fuel pumpmay include a pump piston coupled to a piston stem of substantially thesame exterior diameter as the pump piston. By using a piston stem with asimilar exterior diameter as the pump piston, pump reflux from the steproom may be reduced. In this case, the volume of the step room may notvary significantly during pump strokes. Further, without a significantchange in the volume of the step room, fuel circulation through the steproom may be reduced, and step room cooling may not occur.

The inventors herein have recognized the above issue and identified anapproach to at least partly address the above issue. In one exampleapproach, a method may comprise, when a spill valve is in a pass-throughstate, circulating a portion of fuel from a compression chamber of adirect injection pump to a step room of the direct injection pump, thecirculating including flowing the portion of fuel through the spillvalve and drawing the portion of fuel into the step room from upstreamof the spill valve and downstream of an accumulator. In this way, thestep room may be cooled by reflux fuel from the compression chamber.

In another example approach, a system may comprise an engine, a liftpump, a direct injection fuel pump including a piston coupled to apiston stem, a compression chamber, a step room, and a cam for drivingthe piston, a high pressure fuel rail fluidically coupled to an outletof the direct injection fuel pump, a solenoid activated check valvepositioned at an inlet of the direct injection fuel pump, a fuel supplyline fluidically coupling the lift pump and the solenoid activated checkvalve, an accumulator positioned upstream of the solenoid activatedcheck valve, the accumulator fluidically communicating with the fuelsupply line, a first check valve coupled to the fuel supply line betweenthe accumulator and the solenoid activated check valve, a first fuelconduit including a second check valve, a first end of the first fuelconduit fluidically coupled to the fuel supply line between the firstcheck valve and the solenoid activated check valve, a second end of thefirst fuel conduit fluidically coupled to an inlet of the step room, asecond fuel conduit, a first end of the second fuel conduit fluidicallycoupled to an outlet of the step room, and a second end of the secondfuel conduit fluidically coupled to the fuel supply line at theaccumulator upstream of the first check valve and downstream of a thirdcheck valve. This example system may enable isothermal fuel flow throughthe direct injection fuel pump.

For example, a direct injection (DI) fuel pump of a fuel system in aPFDI or a DI engine may include a compression chamber, a pump pistoncoupled to a piston stem, and a step room. In one example, the pistonstem may have an external diameter that is substantially equal to anexternal diameter of the pump piston. The DI fuel pump may receive fuelinto its compression chamber via a fuel supply line from a lift pump. Anelectronically controlled solenoid activated check valve, fluidicallycoupled to the fuel supply line, may be arranged at an inlet of thecompression chamber of the DI fuel pump. An accumulator may bepositioned upstream of the solenoid activated check valve to store fuelduring a compression stroke in the DI fuel pump. A first check valvelocated between the accumulator and the solenoid activated check valvemay obstruct fuel flow from the solenoid activated check valve to theaccumulator while allowing fuel flow from the accumulator towards thesolenoid activated check valve. Further, the step room may fluidicallycommunicate with the fuel supply line via each of a first fuel conduitand a second fuel conduit. The first fuel conduit may fluidically couplean inlet of the step room to the fuel supply line between the firstcheck valve and the solenoid activated check valve. The second fuelconduit may enable fluidic communication between an outlet of the steproom and the fuel supply line at the accumulator. Further, a third checkvalve may be coupled to the fuel supply line downstream of the lift pumpand upstream of a node where the second fuel conduit merges with thefuel supply line at the accumulator. Thus, when the solenoid activatedcheck valve is de-energized to a pass-through state, a quantity of fuel(e.g., reflux fuel) may exit the compression chamber of the DI fuel pumpthrough the solenoid activated check valve. As such, the quantity offuel may exit the compression chamber during a compression stroke in thedirect injection fuel pump. Since the first check valve impedes fuelflow towards the accumulator, the quantity of fuel may initially flow tothe step room via the first fuel conduit. The quantity of fuel may thenflow from the step room towards the accumulator via the second fuelconduit. Thus, the circulatory flow of the quantity of fuel may cool thestep room.

In this way, fuel heating within the step room of the DI fuel pump maybe reduced. By flowing fuel from the compression chamber to the steproom, pump strokes within the compression chamber (and not within thestep room) may drive fuel flow through the step room. Thus, fuel withinthe DI fuel pump may be maintained substantially isothermal. By reducingfuel heating in the step room, fuel vaporization within the step roommay be diminished leading to enhanced DI fuel pump performance. Overall,durability of the DI fuel pump may be extended, and maintenance costsmay be decreased.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an example embodiment of a cylinder in aninternal combustion engine.

FIG. 2 schematically illustrates an example embodiment of a fuel systemthat may be used in the engine of FIG. 1.

FIG. 3 presents an example embodiment of a high pressure pump inaccordance with the present disclosure.

FIG. 4 demonstrates an example fuel flow during a suction stroke in thehigh pressure pump of FIG. 3.

FIG. 5 depicts an example fuel flow during a compression stroke in thehigh pressure pump of FIG. 3.

FIG. 6 shows an example bell mouth orifice that may be used in the highpressure pump of FIG. 3.

FIG. 7 presents an example flow chart illustrating a control operationof a solenoid activated check valve in the high pressure pump.

FIG. 8 depicts an example flow chart describing fuel flow within thehigh pressure pump of FIG. 3 during different modes.

FIG. 9 shows an example flow chart illustrating reflux fuel flow duringa compression stroke within the high pressure pump of FIG. 3.

DETAILED DESCRIPTION

In port fuel direct injection (PFDI) engines, a fuel delivery system mayinclude multiple fuel pumps for providing a desired fuel pressure to thefuel injectors. As one example, the fuel delivery system may include alower pressure fuel pump (or lift pump) and a higher pressure (or directinjection) fuel pump arranged between a fuel tank and fuel injectors.The higher pressure fuel pump may be coupled upstream of a high pressurefuel rail in a direct injection system to raise a pressure of the fueldelivered to engine cylinders through direct injectors. A solenoidactivated inlet check valve, solenoid activated check valve, or spillvalve, may be coupled upstream of the high pressure (HP) pump toregulate fuel flow into a compression chamber of the high pressure pump.The spill valve is commonly electronically controlled by a controllerwhich may be part of a control system for the engine of the vehicle.Furthermore, the controller may also have a sensory input from a sensor,such as an angular position sensor, that allows the controller tocommand activation of the spill valve in synchronism with a driving camthat powers the high pressure pump.

The following description relates to systems and methods for cooling adirect injection (DI) fuel pump. The DI fuel pump may be included in afuel system, such as the example fuel system of FIG. 2. Further, thefuel system may fuel an engine system such as the example engine systemof FIG. 1. The DI fuel pump may be operated either in a variablepressure mode or in a default pressure mode (FIG. 7). The variablepressure mode may include energizing a solenoid activated check valve(SACV) to regulate fuel volume and pressure in a DI fuel rail. Thedefault pressure mode may include de-energizing the SACV through anentire pump stroke. Fuel may be delivered to a compression chamber ofthe DI fuel pump during an intake stroke of the DI fuel pump (FIG. 4)from a lift pump and/or an accumulator located downstream of the liftpump. During either mode of pump operation, fuel from the compressionchamber of the DI fuel pump (FIG. 3) may exit the compression chamberthrough the SACV when it is in a pass-through state. Specifically, fuelmay exit the compression chamber through the SACV during a compressionstroke in the DI fuel pump as reflux fuel. Further, the reflux fuel mayflow from the SACV to a step room of the DI fuel pump (FIG. 5) andthereon towards the accumulator (FIG. 9). The flow of reflux fuel may beenabled by one or more check valves. These check valves may be replacedby bell mouth orifices, such as the example bell mouth orifice shown inFIG. 6. Fuel flow in the DI fuel pump of the present disclosure duringeach of the variable mode operation and default pressure mode operationis described in FIG. 8.

Regarding terminology used throughout this detailed description, a highpressure pump, or direct injection fuel pump, may be abbreviated as a HPpump (alternatively, HPP) or a DI fuel pump respectively. Accordingly,HPP and DI fuel pump may be used interchangeably to refer to the highpressure direct injection fuel pump. Similarly, a low pressure pump, mayalso be referred to as a lift pump. Further, the low pressure pump maybe abbreviated as LP pump or LPP. Port fuel injection may be abbreviatedas PFI while direct injection may be abbreviated as DI. Also, fuel railpressure, or the value of pressure of fuel within the fuel rail (mostoften the direct injection fuel rail), may be abbreviated as FRP. Thedirect injection fuel rail may also be referred to as a high pressurefuel rail, which may be abbreviated as HP fuel rail. Also, the solenoidactivated inlet check valve for controlling fuel flow into the HP pumpmay be referred to as a spill valve, a solenoid activated check valve(SACV), electronically controlled solenoid activated inlet check valve,and also as an electronically controlled valve. Further, when thesolenoid activated inlet check valve is activated, the HP pump isreferred to as operating in a variable pressure mode. Further, thesolenoid activated check valve may be maintained in its activated statethroughout the operation of the HP pump in variable pressure mode. Ifthe solenoid activated check valve is deactivated and the HP pump relieson mechanical pressure regulation without any commands to theelectronically-controlled spill valve, the HP pump is referred to asoperating in a mechanical mode or in a default pressure mode. Further,the solenoid activated check valve may be maintained in its deactivatedstate throughout the operation of the HP pump in default pressure mode.

FIG. 1 depicts an example of a combustion chamber or cylinder ofinternal combustion engine 10. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder 14(herein also termed combustion chamber 14) of engine 10 may includecombustion chamber walls 136 with piston 138 positioned therein. Piston138 may be coupled to crankshaft 140 so that reciprocating motion of thepiston is translated into rotational motion of the crankshaft.Crankshaft 140 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system (not shown). Further, astarter motor (not shown) may be coupled to crankshaft 140 via aflywheel (not shown) to enable a starting operation of engine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passages 142, 144, and 146 can communicatewith other cylinders of engine 10 in addition to cylinder 14. In someexamples, one or more of the intake passages may include a boostingdevice such as a turbocharger or a supercharger. For example, FIG. 1shows engine 10 configured with a turbocharger including a compressor174 arranged between intake air passages 142 and 144, and an exhaustturbine 176 arranged along exhaust passage 158. Compressor 174 may be atleast partially powered by exhaust turbine 176 via a shaft 180 where theboosting device is configured as a turbocharger. However, in otherexamples, such as where engine 10 is provided with a supercharger,exhaust turbine 176 may be optionally omitted, where compressor 174 maybe powered by mechanical input from a motor or the engine. A throttle162 including a throttle plate 164 may be provided along an intakepassage of the engine for varying the flow rate and/or pressure ofintake air provided to the engine cylinders. For example, throttle 162may be positioned downstream of compressor 174 as shown in FIG. 1, oralternatively may be provided upstream of compressor 174.

Exhaust manifold 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 158 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some examples, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via actuator 152.Similarly, exhaust valve 156 may be controlled by controller 12 viaactuator 154. During some conditions, controller 12 may vary the signalsprovided to actuators 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve150 and exhaust valve 156 may be determined by respective valve positionsensors (not shown). The valve actuators may be of the electric valveactuation type or cam actuation type, or a combination thereof. Theintake and exhaust valve timing may be controlled concurrently or any ofa possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. Each cam actuation system may include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.For example, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT. In other examples, theintake and exhaust valves may be controlled by a common valve actuatoror actuation system, or a variable valve timing actuator or actuationsystem.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. In one example, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some examples, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some examples, each cylinder of engine 10 may be configured with oneor more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including two fuel injectors 166 and 170.Fuel injectors 166 and 170 may be configured to deliver fuel receivedfrom fuel system 8. As elaborated in FIG. 2, fuel system 8 may includeone or more fuel tanks, fuel pumps, and fuel rails. Fuel injector 166 isshown coupled directly to cylinder 14 for injecting fuel directlytherein in proportion to the pulse width of signal FPW-1 received fromcontroller 12 via electronic driver 168. In this manner, fuel injector166 provides what is known as direct injection (hereafter referred to as“DI”) of fuel into cylinder 14. While FIG. 1 shows injector 166positioned to one side of cylinder 14, it may alternatively be locatedoverhead of the piston, such as near the position of spark plug 192.Such a position may improve mixing and combustion when operating theengine with an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a fuel tank of fuel system 8 via a high pressurefuel pump, and a fuel rail. Further, the fuel tank may have a pressuretransducer providing a signal to controller 12.

Fuel injector 170 is shown arranged in intake air passage 146, ratherthan in cylinder 14, in a configuration that provides what is known asport injection of fuel (hereafter referred to as “PFI”) into the intakeport upstream of cylinder 14. Fuel injector 170 may inject fuel,received from fuel system 8, in proportion to the pulse width of signalFPW-2 received from controller 12 via electronic driver 171. Note that asingle electronic driver 168 or 171 may be used for both fuel injectionsystems, or multiple drivers, for example electronic driver 168 for fuelinjector 166 and electronic driver 171 for fuel injector 170, may beused, as depicted.

In an alternate example, each of fuel injectors 166 and 170 may beconfigured as direct fuel injectors for injecting fuel directly intocylinder 14. In another example, each of fuel injectors 166 and 170 maybe configured as port fuel injectors for injecting fuel upstream ofintake valve 150. In yet other examples, cylinder 14 may include only asingle fuel injector that is configured to receive different fuels fromthe fuel systems in varying relative amounts as a fuel mixture, and isfurther configured to inject this fuel mixture either directly into thecylinder as a direct fuel injector or upstream of the intake valves as aport fuel injector. In still another example, cylinder 14 may be fueledsolely by fuel injector 166, or solely by direct injection. As such, itshould be appreciated that the fuel systems described herein should notbe limited by the particular fuel injector configurations describedherein by way of example.

Fuel may be delivered by both injectors to the cylinder during a singlecycle of the cylinder. For example, each injector may deliver a portionof a total fuel injection that is combusted in cylinder 14. Further, thedistribution and/or relative amount of fuel delivered from each injectormay vary with operating conditions, such as engine load, knock, andexhaust temperature, such as described herein below. The port injectedfuel may be delivered during an open intake valve event, closed intakevalve event (e.g., substantially before the intake stroke), as well asduring both open and closed intake valve operation. Similarly, directlyinjected fuel may be delivered during an intake stroke, as well aspartly during a previous exhaust stroke, during the intake stroke, andpartly during the compression stroke, for example. As such, even for asingle combustion event, injected fuel may be injected at differenttimings from the port and direct injector. Furthermore, for a singlecombustion event, multiple injections of the delivered fuel may beperformed per cycle. The multiple injections may be performed during thecompression stroke, intake stroke, or any appropriate combinationthereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such, each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc. It will beappreciated that engine 10 may include any suitable number of cylinders,including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders. Further, each ofthese cylinders can include some or all of the various componentsdescribed and depicted by FIG. 1 with reference to cylinder 14.

Fuel injectors 166 and 170 may have different characteristics. Theseinclude differences in size, for example, one injector may have a largerinjection hole than the other. Other differences include, but are notlimited to, different spray angles, different operating temperatures,different targeting, different injection timing, different spraycharacteristics, different locations etc. Moreover, depending on thedistribution ratio of injected fuel among injectors 170 and 166,different effects may be achieved.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown asnon-transitory read only memory chip 110 in this particular example forstoring executable instructions, random access memory 112, keep alivememory 114, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold.

FIG. 2 schematically depicts an example fuel system 8 of FIG. 1. Fuelsystem 8 may be operated to deliver fuel from a fuel tank 202 to directfuel injectors 252 and port injectors 242 of an engine, such as engine10 of FIG. 1. Fuel system 8 may be operated by a controller, such ascontroller 12 of FIG. 1, to perform some or all of the operationsdescribed with reference to the example routines depicted in FIGS. 4 and5.

Fuel system 8 can provide fuel to an engine, such as example engine 10of FIG. 1, from a fuel tank 202. By way of example, the fuel may includeone or more hydrocarbon components, and may also include an alcoholcomponent. Under some conditions, this alcohol component can provideknock suppression to the engine when delivered in a suitable amount, andmay include any suitable alcohol such as ethanol, methanol, etc. Sincealcohol can provide greater knock suppression than some hydrocarbonbased fuels, such as gasoline and diesel, due to the increased latentheat of vaporization and charge cooling capacity of the alcohol, a fuelcontaining a higher concentration of an alcohol component can beselectively used to provide increased resistance to engine knock duringselect operating conditions.

As another example, the alcohol (e.g., methanol, ethanol) may have wateradded to it. As such, water reduces the alcohol fuel's flammabilitygiving an increased flexibility in storing the fuel. Additionally, thewater content's heat of vaporization enhances the ability of the alcoholfuel to act as a knock suppressant. Further still, the water content canreduce the fuel's overall cost. As a specific non-limiting example, fuelmay include gasoline and ethanol, (e.g., E10, and/or E85). Fuel may beprovided to fuel tank 202 via fuel filling passage 204.

A low pressure fuel pump 208 (herein, also termed lift pump 208) incommunication with fuel tank 202 may be operated to supply fuel fromfuel tank 202 to a first group of port injectors 242, via a first fuelpassage 230. Lift pump 208 may also be referred to as LPP 208, or a LP(low pressure) pump 208. In one example, LPP 208 may be anelectrically-powered lower pressure fuel pump disposed at leastpartially within fuel tank 202. Fuel lifted by LPP 208 may be suppliedat a lower pressure into a first fuel rail 240 coupled to one or morefuel injectors of first group of port injectors 242 (herein alsoreferred to as first injector group). An LPP check valve 209 may bepositioned at an outlet of the LPP. LPP check valve 209 may direct fuelflow from LPP 208 to first fuel passage 230 and second fuel passage 290,and may block fuel flow from first and second fuel passages 230 and 290respectively back to LPP 208.

While first fuel rail 240 is shown dispensing fuel to four fuelinjectors of first group of port injectors 242, it will be appreciatedthat first fuel rail 240 may dispense fuel to any suitable number offuel injectors. As one example, first fuel rail 240 may dispense fuel toone fuel injector of first group of port injectors 242 for each cylinderof the engine. Note that in other examples, first fuel passage 230 mayprovide fuel to the fuel injectors of first group of port injectors 242via two or more fuel rails. For example, where the engine cylinders areconfigured in a V-type configuration, two fuel rails may be used todistribute fuel from the first fuel passage to each of the fuelinjectors of the first injector group.

Direct injection fuel pump 228 (or DI pump 228 or high pressure pump228) is included in second fuel passage 232 and may receive fuel via LPP208. In one example, direct injection fuel pump 228 may be amechanically-powered positive-displacement pump. Direct injection fuelpump 228 may be in communication with a group of direct fuel injectors252 via a second fuel rail 250. Second fuel rail 250 may be a high (orhigher) pressure fuel rail. Second fuel rail 250 may also be termeddirect injection (DI) fuel rail 250. Direct injection fuel pump 228 mayfurther be in fluidic communication with first fuel passage 230 viasecond fuel passage 290. Thus, fuel at lower pressure lifted by LPP 208may be further pressurized by direct injection fuel pump 228 so as tosupply higher pressure fuel for direct injection to second fuel rail 250coupled to one or more direct fuel injectors 252 (herein also referredto as second injector group). In some examples, a fuel filter (notshown) may be disposed upstream of direct injection fuel pump 228 toremove particulates from the fuel.

The various components of fuel system 8 communicate with an enginecontrol system, such as controller 12. For example, controller 12 mayreceive an indication of operating conditions from various sensorsassociated with fuel system 8 in addition to the sensors previouslydescribed with reference to FIG. 1. The various inputs may include, forexample, an indication of an amount of fuel stored in fuel tank 202 viafuel level sensor 206. Controller 12 may also receive an indication offuel composition from one or more fuel composition sensors, in additionto, or as an alternative to, an indication of a fuel composition that isinferred from an exhaust gas sensor (such as sensor 128 of FIG. 1). Forexample, an indication of fuel composition of fuel stored in fuel tank202 may be provided by fuel composition sensor 210. Fuel compositionsensor 210 may further comprise a fuel temperature sensor. Additionallyor alternatively, one or more fuel composition sensors may be providedat any suitable location along the fuel passages between the fuelstorage tank and the two fuel injector groups. For example, fuelcomposition sensor 238 may be provided at first fuel rail 240 or alongfirst fuel passage 230, and/or fuel composition sensor 248 may beprovided at second fuel rail 250 or along second fuel passage 232. As anon-limiting example, the fuel composition sensors can providecontroller 12 with an indication of a concentration of a knocksuppressing component contained in the fuel or an indication of anoctane rating of the fuel. For example, one or more of the fuelcomposition sensors may provide an indication of an alcohol content ofthe fuel.

Note that the relative location of the fuel composition sensors withinthe fuel delivery system can provide different advantages. For example,fuel composition sensors 238 and 248, arranged at the fuel rails oralong the fuel passages coupling the fuel injectors with fuel tank 202,can provide an indication of a fuel composition before being deliveredto the engine. In contrast, fuel composition sensor 210 may provide anindication of the fuel composition at the fuel tank 202.

Fuel system 8 may also comprise pressure sensor 234 coupled to secondfuel passage 290, and pressure sensor 236 coupled to second fuel rail250. Pressure sensor 234 may be used to determine a fuel line pressureof second fuel passage 290 which may correspond to a delivery pressureof low pressure pump 208. Pressure sensor 236 may be positioneddownstream of DI fuel pump 228 in second fuel rail 250 and may be usedto measure fuel rail pressure (FRP) in second fuel rail 250. Additionalpressure sensors may be positioned in fuel system 8 such as at the firstfuel rail 240 to measure the pressure therein. Sensed pressures atdifferent locations in fuel system 8 may be communicated to controller12.

LPP 208 may be used for supplying fuel to both the first fuel rail 240during port fuel injection and the DI fuel pump 228 during directinjection of fuel. During both port fuel injection and direct injectionof fuel, LPP 208 may be controlled by controller 12 to supply fuel tothe first fuel rail 240 and/or the DI fuel pump 228 based on fuel railpressure in each of first fuel rail 240 and second fuel rail 250.

In one example, during port fuel injection, controller 12 may controlLPP 208 to operate in a continuous mode to supply fuel at a constantfuel pressure to first fuel rail 240 so as to maintain a relativelyconstant port fuel injection pressure.

On the other hand, during direct injection of fuel when port fuelinjection is OFF and deactivated, controller 12 may control LPP 208 tosupply fuel to the DI fuel pump 228. LPP 208 may be operated in a pulsedmode, where the LPP is alternately switched ON and OFF based on fuelpressure readings from pressure sensor 236 coupled to second fuel rail250. In an alternate embodiment, LPP 208 may be operated in pulsed modeduring both PFI and DI engine operations to benefit from reduced powerconsumption of the lift pump when operated in the pulsed mode.

As such, LPP 208 and the DI fuel pump 228 may be operated to maintain aprescribed fuel rail pressure in second fuel rail 250. Pressure sensor236 coupled to the second fuel rail 250 may be configured to provide anestimate of the fuel pressure available at the group of direct injectors252. Then, based on a difference between the estimated rail pressure anda desired rail pressure, each of the pump outputs may be adjusted.

Controller 12 can also control the operation of each of fuel pumps LPP208 and DI fuel pump 228 to adjust an amount, pressure, flow rate, etc.,of a fuel delivered to the engine. As one example, controller 12 canvary a pressure setting, a pump stroke amount, a pump duty cyclecommand, and/or fuel flow rate of the fuel pumps to deliver fuel todifferent locations of the fuel system. As one example, a DI fuel pumpduty cycle may refer to a fractional amount of a full DI fuel pumpvolume to be pumped. Thus, a 10% DI fuel pump duty cycle may representenergizing a solenoid activated check valve such that 10% of the DI fuelpump volume may be pumped. A driver (not shown) electronically coupledto controller 12 may be used to send a control signal to LPP 208, asrequired, to adjust the output (e.g., speed, delivery pressure) of theLPP 208. The amount of fuel that is delivered to the group of directinjectors via the DI fuel pump 228 may be adjusted by adjusting andcoordinating the output of the LPP 208 and the DI fuel pump 228.

FIG. 3 illustrates example DI fuel pump 228 (also termed, DI pump 228)shown in the fuel system 8 of FIG. 2. As mentioned earlier in referenceto FIG. 2, DI pump 228 receives fuel at a lower pressure from LPP 208via second fuel passage 290. Further, DI pump 228 pressurizes the fuelto a higher pressure before pumping the fuel to second group ofinjectors 252 (or direct injectors) via second fuel passage 232. Inlet303 of compression chamber 308 in DI pump 228 is supplied fuel via lowpressure fuel pump 208 as shown in FIG. 3. The fuel may be pressurizedupon its passage through direct injection fuel pump 228 and may besupplied to second fuel rail 250 and direct injectors 252 through pumpoutlet 304.

In the depicted example, direct injection pump 228 may be an enginedriven displacement pump that includes a pump piston 306 and piston rod320 (also termed, piston stem 320), a pump compression chamber 308(herein also referred to as compression chamber), bore 350, and a steproom 318. Pump piston 306 may move axially (e.g., in a reciprocatingmotion) within bore 350. Assuming that pump piston 306 is substantiallyat a bottom dead center (BDC) position in FIG. 3, the pump displacementmay be represented as displacement volume 377. The displacement of theDI pump may be measured as the area swept by pump piston 306 as it movesfrom top dead center (TDC) to BDC or vice versa. A second volume alsoexists within compression chamber 308, the second volume being aclearance volume 378 of the pump. Clearance volume 378 of the pump mayalso be known as dead volume 378. The clearance volume defines theregion in compression chamber 308 that remains when pump piston 306 isat TDC. In other words, the addition of displacement volume 377 andclearance volume 378 form compression chamber 308.

Pump piston 306 includes a piston top 305 and a piston bottom 307. Pumppiston 306 may be coupled (e.g., mechanically) to piston rod 320. In theexample embodiment of FIG. 3, piston rod 320 may have an externaldiameter that is substantially the same as an external diameter of pumppiston 306. By enlarging a width of the piston rod 320 to substantiallythe same as a width of pump piston 306, pump reflux from step room 318may be reduced.

Reflux may occur in piston-operated pumps (e.g., a DI pump with pumppiston coupled to a piston stem that is narrower relative to an externaldiameter of the pump piston) wherein a portion of the pumped liquid(fuel in this case) is repeatedly forced into and out of the step roominto a low pressure fuel line. The progression of pump reflux may bedescribed as follows: during the compression stroke in the DI fuel pump,as the pump piston is traveling from bottom dead center (BDC) to topdead center (TDC), fluid may be sucked from low pressure fuel line(e.g., fuel supply line 344) to the step room or volume under thepiston. During the pump's suction (intake) stroke, as the pump piston istraveling from TDC to BDC, fluid may be forced from the bottom of thepiston (the volume under the piston, step room) toward the low pressurefuel supply line.

Pump reflux may excite the natural frequency of the low pressure fuelsupply line. The repeated, reversing fuel flow from the bottom of thepiston may create fuel pressure and flow pulsations that may at leastpartially cause a number of issues. One of these issues may be increasednoise caused by the flow pulsations, thereby requiring additional soundreduction components that may otherwise be unnecessary.

Pump reflux from the step room may be reduced by incorporating a widerpiston rod (e.g., piston rod with a larger diameter) in the DI fuelpump. As shown in FIG. 3, DI fuel pump 228 includes piston rod 320 withan outside diameter that is equal or substantially equal to the outsidediameter of pump piston 306. To easily differentiate between the stemand piston in FIG. 3, the diameter of piston stem 320 is shown to beslightly smaller than the diameter of pump piston 306, when in realitythe diameters may be equal.

Thus, step room 318 may be occupied largely by piston stem 320, therebysignificantly reducing the variable volume of step room 318 on thebackside of pump piston 306. In other words, a smaller vacuous volume ispresent on the backside of pump piston 306 in between the bore and thepiston stem (e.g., within the step room) throughout the movement of thepump piston. In this way, as pump piston 306 and the piston stem 320move from TDC to BDC and vice versa, pump reflux on the underside ofpump piston 306 (e.g., from step room 318) may be significantly reduced.

In an alternative embodiment, the piston stem 320 may have an exteriordiameter that is approximately half (e.g. 50%) the exterior diameter ofpump piston 306 to reduce pump reflux from the step room 318.

The step room 318 and compression chamber 308 may include respectivecavities positioned on opposing sides of the pump piston 306. Toelaborate, step room 318 may be a variable volume region formedunderneath piston bottom 307 (as depicted in FIG. 3). Further,compression chamber 308 may be a chamber of variable volume formed abovepiston top 305 of pump piston 306 (as shown in FIG. 3). Other examplepositions of the step room and compression chamber are possible relativeto pump piston 306 without departing from the scope of this disclosure.Step room 318 may surround piston stem 320. It will also be noted thatstep room 318 is largely consumed by piston stem 320.

In one example, driving cam 310 may be in contact with piston rod 320 ofthe DI pump 228 and may be configured to drive pump piston 306 from BDCto TDC and vice versa, thereby creating the motion necessary to pumpfuel through compression chamber 308. Driving cam 310 includes fourlobes and completes one rotation for every two engine crankshaftrotations. A cam follower, e.g., a roller-follower, may be positionedbetween the piston stem 320 and driving cam 310.

Pump piston 306 reciprocates up and down within bore 350 of DI fuel pump228 to pump fuel. DI fuel pump 228 is in a compression stroke when pumppiston 306 is traveling in a direction that reduces the volume ofcompression chamber 308. Conversely, direct fuel injection pump 228 isin a suction stroke or an intake stroke when pump piston 306 istraveling in a direction that increases the volume of compressionchamber 308.

A solenoid activated check valve (SACV) 312 is positioned upstream ofinlet 303 to compression chamber 308 of DI pump 228. SACV 312 may alsobe termed spill valve 312. Controller 12 may be configured to regulatefuel flow through solenoid activated check valve 312 by energizing orde-energizing a solenoid within SACV 312 (based on the solenoid valveconfiguration) in synchronism with the driving cam 310. Accordingly,SACV 312 may be operated in two distinct, albeit, potentiallyoverlapping, modes. In a first mode (e.g., a variable pressure mode),SACV 312 is actuated to limit (e.g., inhibit) the amount of fueltraveling through the SACV to upstream of the SACV 312. To elaborate,the SACV may obstruct fuel flow from compression chamber 308 throughSACV 312 to upstream of SACV 312. In the first mode, fuel may flowthrough SACV 312 from upstream of SACV 312 to downstream of SACV 312. Ina second mode (e.g., a default pressure mode), SACV 312 is effectivelydisabled and fuel can travel through SACV 312 both upstream anddownstream of SACV 312. While SACV 312 has been described as above, italso can be implemented as a solenoid plunger that forces a check valveopen when de-energized. This plunger design may have an additionaladvantage of being able to de-energize the solenoid once pressure buildsin the compression chamber 308, thus holding the check valve closed.

As mentioned earlier, SACV 312 may be configured to regulate the mass(or volume) of fuel compressed within DI fuel pump 228. In one example,controller 12 may adjust a closing timing of the SACV to regulate themass of fuel compressed. For example, closing the SACV 312 at a latertime relative to piston compression (e.g., as volume of compressionchamber is decreasing) may reduce the amount of fuel mass delivered fromthe compression chamber 308 to pump outlet 304 since more of the fueldisplaced from the compression chamber 308 can flow through the SACV 312before it closes. Herein, the SACV may be in a pass-through stateallowing fuel to flow from compression chamber 308 through SACV 312 toupstream of SACV 312, until the SACV 312 is closed. For example, a 30%duty cycle operation of the DI pump may include closing the SACV 312when the compression stroke is about 70% complete (e.g., a laterclosing). In other words, the 30% duty cycle operation may includeclosing the SACV 312 when 70% of the fuel in the compression chamber isexpelled through the SACV 312 and 30% fuel is retained in thecompression chamber. Thus, the 30% duty cycle operation delivers about30% of the DI fuel pump volume into the DI fuel rail 250.

In contrast, an early closing of the solenoid activated inlet checkvalve relative to piston compression (e.g., as volume of compressionchamber is decreasing) may increase the amount of fuel mass deliveredfrom the compression chamber 308 to the pump outlet 304 since less ofthe fuel displaced from the compression chamber 308 can flow (in reversedirection) through the electronically controlled check valve 312 beforeit closes. An example of early closing of the SACV may occur during an80% duty cycle operation of the DI fuel pump. Herein the SACV 312 may beclosed early in the compression stroke, e.g., when 20% of thecompression stroke is complete. To elaborate, the 80% duty cycleoperation of the DI pump may include closing the SACV 312 when about 20%of the DI fuel pump volume is expelled from the compression chamberthrough the SACV 312. Thus, 80% of the DI fuel pump volume may bedelivered to the DI fuel rail 250 via pump outlet 304.

Opening and closing timings of the SACV 312 may be coordinated withstroke timings of the DI fuel pump 228. Alternately or additionally, bycontinuously throttling fuel flow into the DI fuel pump from the lowpressure fuel pump, fuel ingested into the direct injection fuel pumpmay be regulated without use of SACV 312.

Pump inlet 399 may receive fuel from an outlet of LPP 208 via secondfuel passage 290 and may direct the fuel along first section 343 of fuelsupply line 344 to SACV 312 via third check valve 321 and first checkvalve 322. First section 343 of fuel supply line 344 extends from pumpinlet 399 until node 362. Further, third check valve 321 is coupled tofirst section 343 of fuel supply line 344 downstream of pump inlet 399and upstream of node 362. As such, node 362 includes a node whereaccumulator 330 is fluidically coupled to fuel supply line 344. Thirdcheck valve 321 enables fuel to flow from pump inlet 399 towards node362 and SACV 312 along fuel supply line 344. Further, third check valve321 obstructs the flow of fuel from node 362 towards pump inlet 399 andLPP 208.

First check valve 322 is positioned upstream of SACV 312 along fuelsupply line 344. First check valve 322 is biased to impede fuel flow outof SACV 312 towards accumulator 330, third check valve 321, and pumpinlet 399. First check valve 322 allows fuel flow from the low pressurepump 208 to SACV 312. Further still, first check valve allows fuel flowfrom accumulator 330 to SACV 312. Accumulator 330 may store fuel duringat least a portion of a compression stroke in the DI fuel pump 228 andmay release the stored fuel during at least a portion of an intakestroke in the DI fuel pump 228.

When solenoid activated check valve 312 is deactivated (e.g., notelectrically energized), and DI fuel pump 228 is operating in the secondmode (such as the default pressure mode), solenoid activated check valve312 operates in a pass-through state allowing fuel to flow through SACV312 both upstream and downstream of SACV 312. Further, pressure in theDI fuel pump 228 may be maintained at a default pressure via accumulator330. Accumulator 330 is a pressure accumulator positioned along fuelsupply line 344 upstream of each of first check valve 322 and SACV 312and downstream of third check valve 321. As depicted, first check valveis arranged between accumulator 330 and SACV 312 while third check valve321 is positioned between pump inlet 399 and accumulator 330. In oneexample, accumulator 330 is a 15 bar (absolute) accumulator. In anotherexample, accumulator 330 is a 20 bar (absolute) accumulator. As such,accumulator 330 may be a pre-loaded accumulator.

The default pressure in DI fuel pump 228 in the default pressure modemay be based on a pressure rating of accumulator 330. Specifically, thedefault pressure may be based on a force constant of a spring 334coupled to a piston 336 within accumulator 330. As depicted in FIG. 3,accumulator 330 includes a first variable volume 340 formed underneathpiston 336 and a second variable volume 338 formed above piston 336.Piston 336 may move axially between lower stop 339 and roof 342 ofaccumulator 330 as a fluid is stored in and released from first variablevolume 340. The fluid, such as fuel, may enter accumulator 330 viaentrance 332 and may be stored in first variable volume 340. Secondvariable volume 338 may be formed around spring 334 towards an upperportion of accumulator 330. It will be noted that though accumulator 330is shown as a spring-piston type pressure accumulator, other types ofpressure accumulators known in the art may be used without departingfrom the scope of this disclosure.

Accumulator 330 may also apply a positive pressure across the pumppiston 306 during a portion of the piston intake (suction) stroke,further enhancing Poiseuille lubrication. In addition, a portion ofcompression energy from the positive pressure applied by accumulator 330on pump piston 306 may be transferred to a camshaft of driving cam 310.

Regulating the pressure in compression chamber 308 allows a pressuredifferential to form from piston top 305 to piston bottom 307. Thepressure in step room 318 may be at the pressure of the outlet of thelow pressure pump (e.g., 5 bar) during at least a portion of a pumpstroke while the pressure at piston top 305 is at a regulation pressureof accumulator 330 (e.g., 15 bar). The pressure differential allows fuelto seep from piston top 305 to piston bottom 307 through a clearancebetween pump piston 306 and bore 350, thereby lubricating directinjection fuel pump 228.

During conditions when DI fuel pump operation is regulated mechanically,controller 12 may deactivate solenoid activated inlet check valve 312and accumulator 330 regulates pressure in fuel rail 250 (and compressionchamber 308) to a single substantially constant (e.g., accumulatorpressure±0.5 bar) pressure during most of the compression stroke. On theintake stroke of pump piston 306, the pressure in compression chamber308 drops to a pressure near the pressure of the lift pump 208. Oneresult of this regulation method is that the fuel rail is regulated to aminimum pressure approximately the pressure of accumulator 330. Thus, ifaccumulator 330 has a pressure setting of 15 bar, the fuel rail pressurein second fuel rail 250 becomes 20 bar because the accumulator pressuresetting of 15 bar is added to the 5 bar of lift pump pressure.Specifically, the fuel pressure in compression chamber 308 is regulatedduring the compression stroke of direct injection fuel pump 228. It willbe appreciated that the solenoid activated check valve 312 is maintaineddeactivated (in pass-through state) throughout the operation of the DIfuel pump 228 in the default pressure mode.

A forward flow outlet check valve 316 (also termed, outlet check valve316) may be coupled downstream of pump outlet 304 of the compressionchamber 308 of DI fuel pump 228. Outlet check valve 316 opens to allowfuel to flow from the pump outlet 304 of compression chamber 308 intosecond fuel rail 250 only when a pressure at the pump outlet 304 ofdirect injection fuel pump 228 (e.g., a compression chamber outletpressure) is higher than the fuel rail pressure. In another example DIfuel pump, inlet 303 to compression chamber 308 and pump outlet 304 maybe the same port.

A fuel rail pressure relief valve 314 is located parallel to outletcheck valve 316 in a parallel passage 319 that branches off from secondfuel passage 232. Fuel rail pressure relief valve 314 may allow fuelflow out of fuel rail 250 and passage 232 into compression chamber 308when pressure in parallel passage 319 and second fuel passage 232exceeds a predetermined pressure, where the predetermined pressure maybe a relief pressure setting of fuel rail pressure relief valve 314. Assuch, fuel rail pressure relief valve 314 may regulate pressure in fuelrail 250. Fuel rail pressure relief valve 314 may be set at a relativelyhigh relief pressure such that it acts only as a safety valve that doesnot affect normal pump and direct injection operation.

During operation in either mode (variable pressure or default pressure),DI fuel pump 228 may form a hot spot on piston bottom 307 of pump piston306. Accordingly, temperature of fuel within step room 318 may increaseresulting in vaporization of fuel and leading to other adverse effectsof fuel vaporization. Fuel in the step room 318 along with the pistonbottom 307 may be cooled by circulating cooler fuel through step room318. For example, a portion of fuel from the compression chamber 308 maybe directed to step room 318 to replace fuel in step room 318 and enablecooling of the piston bottom 307.

Accordingly, the example embodiment of DI fuel pump 228 in FIG. 3includes first fuel conduit 376 fluidically communicating with fuelsupply line 344. To elaborate, a first end 372 of first fuel conduit 376is fluidically coupled to fuel supply line 344 at node 364 wherein node364 is positioned downstream of first check valve 322 and upstream ofSACV 312 relative to fuel flow during an intake stroke in DI pump 228.As such, first end 372 of first fuel conduit 376 is coupled to fuelsupply line 344 between first check valve 322 and SACV 312. First fuelconduit 376 includes second check valve 324 which allows fuel flow fromfuel supply line 344 (e.g., from node 364) towards an inlet 352 of steproom 318. Thus, second check valve 324 obstructs fuel flow from steproom 318 to fuel supply line 344 (e.g., to node 364) via first fuelconduit 376. Further, first fuel conduit 376 is fluidically coupled toinlet 352 of step room 318 via second end 374 of first fuel conduit 376.

When SACV 312 is in the pass-through state, and pump piston 306 is in acompression stroke, a portion of fuel within compression chamber 308 maybe ejected via inlet 303 of compression chamber 308, through SACV 312towards first check valve 322 along fuel supply line 344. Since firstcheck valve 322 impedes fuel flow from SACV 312 towards accumulator 330along fuel supply line 344, the portion of fuel exiting compressionchamber 308 may stream via node 364 into first end 372 of first fuelconduit 376, and through first fuel conduit 376 and second check valve324 into step room 318. The portion of fuel may be received via secondend 374 of first fuel conduit 376 into inlet 352 of step room 318. Theportion of fuel exiting compression chamber 308 during the compressionstroke through SACV 312 may be termed reflux fuel.

An outlet 354 of step room 318 may be fluidically coupled to fuel supplyline 344 at node 362 via second fuel conduit 356. To elaborate, secondfuel conduit 356 may be fluidically coupled to fuel supply line 344 (orfirst section 343 of fuel supply line 344) downstream of third checkvalve 321 at node 362. Fuel from step room 318 including the portion offuel (e.g., reflux fuel) may exit step room 318 via outlet 354 of steproom 318. Further, the portion of fuel may flow into first end 355 ofsecond fuel conduit 356, stream through second fuel conduit 356, andflow towards accumulator 330 which may be coupled to fuel supply line344 at node 362. It will be noted that accumulator 330 is fluidicallycoupled to fuel supply line 344 at node 362 via passage 348. Thus, node362 may include a fluidic coupling between a second end 357 of secondfuel conduit 356, accumulator 330 (via passage 348), first section 343of fuel supply line 344, and fuel supply line 344. Further still, secondend 357 of second fuel conduit 356 intersects fuel supply line 344 atnode 362 positioned upstream of first check valve 322 and downstream ofthird check valve 321 relative to fuel flow from pump inlet 399 towardsSACV 312.

Thus, the portion of fuel (also termed, reflux fuel) may exit step room318 and be returned to each of accumulator 330 and fuel supply line 344via second fuel conduit 356. As such, the portion of fuel may be largelystored within accumulator 330 (e.g., in first variable volume 340)during the remaining duration of the compression stroke. Third checkvalve 321 may block the flow of fuel towards pump inlet 399.Accordingly, a larger proportion of the reflux fuel may be directedtowards accumulator 330 via passage 348.

In this way, fuel may be positively pumped through step room 318 usingreflux fuel flow from compression chamber 308. Specifically, reflux fuelfrom piston top 305 of pump piston 306 is used for circulation andcooling of step room 318. Reflux fuel from the compression chamber 308may be suited for a DI fuel pump which includes a pump piston 306coupled to a piston stem 320 with an exterior diameter that issubstantially the same as the exterior diameter of the pump piston 306.

It will be appreciated that though the depicted example of FIG. 3 showssecond check valve 324 coupled to first fuel conduit 376, in alternateembodiments, second check valve 324 may be instead positioned in secondfuel conduit 356 between outlet 354 of step room 318 and second end 357of second fuel conduit 356. Thus, an example system may comprise anengine, a lift pump, a direct injection fuel pump including a pistoncoupled to a piston stem, a compression chamber, a step room, and a camfor driving the piston, a high pressure fuel rail fluidically coupled toan outlet of the direct injection fuel pump, a solenoid activated checkvalve positioned at an inlet of the direct injection fuel pump, a fuelsupply line fluidically coupling the lift pump and the solenoidactivated check valve, an accumulator positioned upstream of thesolenoid activated check valve, the accumulator fluidicallycommunicating with the fuel supply line, a first check valve coupled tothe fuel supply line between the accumulator and the solenoid activatedcheck valve, a first fuel conduit including a second check valve, afirst end of the first fuel conduit fluidically coupled to the fuelsupply line between the first check valve and the solenoid activatedcheck valve, a second end of the first fuel conduit fluidically coupledto an inlet of the step room, a second fuel conduit, a first end of thesecond fuel conduit fluidically coupled to an outlet of the step room,and a second end of the second fuel conduit fluidically coupled to thefuel supply line at the accumulator upstream of the first check valveand downstream of a third check valve. The system may further comprise acontroller having executable instructions stored in a non-transitorymemory for de-energizing the solenoid activated check valve to functionin a pass-through state. The solenoid activated check valve may bede-energized and may function in the pass-through state for an entirepump stroke during a default pressure mode of operation of the directinjection fuel pump. Further, the solenoid activated check valve may bede-energized and may also function in the pass-through state during aportion of the pump stroke (e.g., an earlier part of the compressionstroke) in variable pressure mode operation of the direct injection fuelpump (e.g., when duty cycle is <100%). During a portion of a compressionstroke in the direct injection fuel pump, reflux fuel from thecompression chamber may flow to the step room via the solenoid activatedcheck valve in the pass-through state, into the first end (e.g., 372) ofthe first fuel conduit (e.g., 376), through the second check valve 324,and via the second end (e.g. 374) of the first fuel conduit 376 into theinlet 352 of the step room 318. The reflux fuel may further stream fromthe outlet 354 of the step room 318 into the first end (e.g., 355) ofthe second fuel conduit 356 towards the accumulator 330 and the fuelsupply line 344 via the second end 357 of the second fuel conduit 356.

It will be appreciated that though the example embodiment shown in FIGS.2 and 3 includes a port fuel direct injection engine, the directinjection fuel pump of the present disclosure may also be suitable for adirect injection engine.

It will be noted that while DI pump 228 is shown in FIG. 2 as a symbolwith no detail, FIG. 3 shows pump 228 in full detail. It will also benoted that each of first fuel conduit 376 and second fuel conduit 356may not include any additional intervening components (e.g., valves,additional passages, etc.) than those described and depicted in FIG. 3.Thus, first fuel conduit 376 fluidically couples step room 318 to fuelsupply line 344 and may include only second check valve 324 coupled tofirst fuel conduit 376. No other component or opening may be included infirst fuel conduit 376 between node 364 and inlet 352 of step room 318.Second fuel conduit 356 fluidically couples outlet 354 of step room 318to each of fuel supply line 344 and accumulator 330 without anyintervening elements or openings within the second fuel conduit 356. Inalternate embodiments, second check valve 324 may be positioned insecond fuel conduit 356. Further, first section 343 of fuel supply line344 may include third check valve 321 alone without additionalcomponents, valves, channels, etc. than that depicted in FIG. 3. Furtherstill, no intervening components, passages, or openings than thosedescribed (and depicted in FIG. 3) may be included in first section 343of fuel supply line 344 between pump inlet 399 and node 362 (other thanthird check valve 321). Additionally, no intervening components,passages, or openings than those described (and depicted in FIG. 3) maybe included in fuel supply line 344 between node 362 and first checkvalve 322, and between first check valve 322 and SACV 312. Thus, firstfuel conduit 376 may be the only channel fluidically coupled betweenfirst check valve 322 and SACV 312. Passage 348 may fluidically coupleaccumulator 330 to fuel supply line 344 at node 362 and second fuelconduit 356 may be fluidically coupled to fuel supply line 344 (and toaccumulator 330) at node 362. Thus, passage 348 and second fuel conduit356 may be the only channels coupled to fuel supply line 344 between DIpump inlet 399 and first check valve 322.

It is further noted here that DI pump 228 of FIG. 3 is presented as anillustrative example of one possible configuration for a DI pump thatcan be operated in an electronic regulation (or variable pressure) modeas well as in a default pressure or mechanically-regulated mode.Components shown in FIG. 3 may be removed and/or changed whileadditional components not presently shown may be added to DI fuel pump228 while still maintaining the ability to deliver high-pressure fuel toa direct injection fuel rail with and without electronic pressureregulation.

Turning now to FIG. 4, it shows an example flow of fuel during an intakestroke (also termed, suction stroke) in DI fuel pump 228. Fuel flow fromthe accumulator (e.g., stored reflux fuel) is depicted as dashed lines(short dashes) and fuel received from the LP pump is depicted as lineswith longer dashes. The direction of fuel flow is indicated by thearrows on the dashed lines.

As shown in FIG. 4, pump piston 306 (and piston stem 320) travelsdownwards in the suction stroke towards bottom dead center (BDC)position such that the volume of compression chamber 308 increases.Further still, pump piston 306 along with piston stem 320 may move(concurrently) away from compression chamber 308 when in the intakestroke. The moment depicted in FIG. 4 may indicate a moment immediatelybefore pump piston 306 reaches BDC position.

As the volume of compression chamber 308 increases, fuel may be drawninto the compression chamber from each of the accumulator 330 (shortdashed lines) and LPP 208 (longer dashes) via first check valve 322 andthrough SACV 312. As depicted, controller 12 may command SACV 312 to thepass-through state during the suction stroke enabling fuel to flow intothe compression chamber 308. Fuel stored in first variable volume 340 ofaccumulator 330 may be drawn towards entrance 332 of accumulator 330 inthe suction stroke. Further, as the stored fuel exits accumulator 330via passage 348, piston 336 of the accumulator may shift downwardstowards lower stop 339 (as shown by bold arrows 402). Stored fuel fromthe accumulator 330 may be released first into fuel supply line 344 (andcompression chamber 308) prior to drawing additional fuel from LPP 208.Alternatively, fuel may be drawn simultaneously (as shown in FIG. 4)from each of LPP 208 and accumulator 330 into compression chamber 308.

Thus, fuel may flow from LPP 208 (via pump inlet 399 through firstsection 343 of fuel supply line 344 past third check valve 321,) andaccumulator 330 (via entrance 332 and passage 348 of accumulator 330)across node 362, into fuel supply line 344 and past first check valve322, via node 364, through SACV 312 into inlet 303 of compressionchamber 308. Further, in the suction stroke there may be no net fuelflow into first fuel conduit 376. There may be no net fuel flow out ofstep room 318 into second fuel conduit 356 during the suction stroke asthe piston rod 320 is substantially the same diameter as the pump piston306. FIG. 5 presents an example flow of fuel during a compression strokein the DI fuel pump 228. The depicted compression stroke in DI fuel pump228 may be a compression stroke subsequent to the suction stroke shownin FIG. 4. Further still, the SACV 312 continues to be open and in itspass-through state, allowing fuel to flow from compression chamber 308to upstream of SACV 312. Herein, the SACV 312 may be held in itspass-through state during either an initial duration of the compressionstroke based on a desired duty cycle, specifically a less than 100% dutycycle, of the DI pump in the variable pressure mode. Alternatively, theSACV 312 may be held in its pass-through state for an entire pump strokeduring the default pressure mode of DI pump operation.

It will be appreciated that if a 100% duty cycle of pump operation iscommanded, SACV 312 may be energized to close at the initiation of thecompression stroke, and there may be no reflux fuel exiting the SACV 312during the compression stroke.

During the compression stroke (also termed, delivery stroke), pumppiston 306 moves towards top dead center (TDC) position such that thevolume of the compression chamber 308 reduces. Accordingly, fuel in thecompression chamber 308 may be expelled from compression chamber 308through SACV 312 towards node 364 in fuel supply line 344. Since firstcheck valve 322 impedes the flow of fuel from SACV 312 (or node 364)towards either accumulator 330 or node 362, fuel may stream into firstend 372 of first fuel conduit 376 at node 364. Fuel expelled fromcompression chamber 308 through SACV 312 during the compression stroke,termed reflux fuel 520, is depicted as dashed lines (medium dashesrelative to large and small dashes of fuel flow in FIG. 4). Reflux fuel520 may flow from compression chamber 308, through SACV 312, past node364, into first end 372 of first fuel conduit 376 and through first fuelconduit 376, across second check valve 324, past second end 374 of firstfuel conduit 376, and into step room 318 via inlet 352 of step room 318.The direction of reflux fuel flow when the SACV 312 is in pass-throughstate is indicated by arrows on the dashed lines representing refluxfuel 520. All fuel flow depicted in FIG. 5 is for reflux fuel flow.

Reflux fuel may enter step room 318 via inlet 352 and may exit step room318 via outlet 354 of step room 318. Outlet 354 of step room 318, in thedepicted example, is positioned opposite from inlet 352 of step room318. In alternative examples, the outlet 354 of step room 318 may bepositioned at a different location than shown in FIG. 5 relative toinlet 352 of step room 318 without departing from the scope of thisdisclosure.

Since piston stem 320 occupies a considerable vacuous volume of steproom 318, reflux fuel 520 from compression chamber 308 arriving in steproom 318 may also exit step room 318 during the compression stroke.Thus, reflux fuel 520 is shown exiting step room 318 via outlet 354 intosecond fuel conduit 356. To elaborate, reflux fuel 520 may stream intosecond fuel conduit 356 via first end 355 of the second fuel conduit356. Further, reflux fuel 520 may flow through second fuel conduit 356to be returned to the fuel supply line 344 via second end 357 of secondfuel conduit 356 at node 362 upstream of first check valve 322. As such,reflux fuel 520 may be returned to fuel supply line 344 at node 362downstream of third check valve 321. Further still, reflux fuel 520 mayflow through passage 348 and enter accumulator 330 since fuel flow toupstream of third check valve 321 towards pump inlet 399 is blocked bythird check valve 321. To elaborate, reflux fuel 520 may flow into firstvariable volume 340 of accumulator 330 via entrance 332. As fuel fillsup first variable volume 340, piston 336 of accumulator 330 may shiftaway from lower stop 339 towards roof 342 (shown by bold arrows 502) ofaccumulator 330 compressing spring 334 within second variable volume338. Thus, reflux fuel 520 may be stored in accumulator 330 during atleast a part of the compression stroke. The stored reflux fuel 520 maybe released into compression chamber 308 during a subsequent intakestroke in the DI fuel pump 228.

Thus, reflux fuel may flow, as shown in FIG. 5, from the compressionchamber 308 of DI fuel pump 228 through spill valve 312, past node 364,through first fuel conduit 376, across second check valve 324, into steproom 318, and thereon via second fuel conduit 356 into accumulator 330.It will be appreciated that reflux fuel may not flow from thecompression chamber 308 into accumulator 330 without first flowingthrough step room 318 (as first check valve 322 obstructs fuel flow fromspill valve 312 towards accumulator 330 and LPP 208).

An example method may, thus, comprise, when a spill valve is in apass-through state, circulating a portion of fuel from a compressionchamber of a direct injection pump to a step room of the directinjection pump, the circulating including flowing the portion of fuelthrough the spill valve and drawing the portion of fuel into the steproom from upstream of the spill valve and downstream of an accumulator.The accumulator (e.g. accumulator 330) may be positioned upstream of thespill valve (e.g., SACV 312), and a first check valve (e.g., first checkvalve 322) may be positioned between the accumulator and the spillvalve. The method may further comprise returning the portion of fuel toa fuel supply line at the accumulator upstream of the first check valve.The drawing of the portion of fuel into the step room from upstream ofthe spill valve and downstream of an accumulator may include drawing theportion of fuel from upstream of the spill valve and downstream of thefirst check valve (such as from node 364). The portion of fuel drawninto the step room (e.g. step room 318) from upstream of the spill valveand downstream of the first check valve may flow through a second checkvalve (such as second check valve 324), the second check valve arrangedupstream of the step room. The portion of fuel may include reflux fuelfrom the compression chamber. Each of the circulating and the returningof the portion of fuel may occur during a compression stroke in thedirect injection fuel pump. Further, the portion of fuel may besubstantially stored in the accumulator during a period of thecompression stroke, and the portion of fuel may be released during aduration of a suction stroke in the pump. In one example, the directinjection fuel pump may include a pump piston coupled to a piston stem,the piston stem having an external diameter that is substantially thesame as an external diameter of the pump piston. In another example, thedirect injection fuel pump may include a pump piston coupled to a pistonstem, the piston stem having an external diameter that is substantiallyhalf the size of an external diameter of the pump piston.

Turning now to FIG. 6, it shows an example bell mouth orifice 600 thatmay be used in the example embodiment of DI fuel pump 228 in FIG. 3 toreplace first check valve 322 and second check valve 324. The bell mouthorifice may be designed such that fuel flows more easily in a firstdirection (e.g., the direction of flow indicated by dashed lines in FIG.6) than in a second direction. The second direction may be opposite tothe first direction. For example, a coefficient of discharge for thebell mouth orifice 600 in the first direction may be 1 while acoefficient of discharge in the second (e.g., opposite to first)direction may be 0.5. By enabling a more rapid fluid flow in the firstdirection contrary to the second direction, bell mouth orifices mayfunction as check valves enabling fluid flow in the first directionwhile impeding fluid flow in the second direction. Further, using twosmaller bell mouth orifices (e.g., bugle-shaped elements) can provide agreater coefficient of discharge directional difference than one largerbugle.

FIG. 7 presents an example routine 700 illustrating an example controlof DI fuel pump operation in the variable pressure mode and in thedefault pressure mode. Specifically, routine 700 includes activating andenergizing a solenoid activated check valve (SACV) at an inlet of thecompression chamber of the DI fuel pump when the DI pump is operating inthe variable pressure mode. The SACV may be energized to closeddependent on a desired duty cycle of pump operation.

At 702, engine operating conditions may be estimated and/or measured.For example, engine conditions such as engine speed, engine fuel demand,boost, driver demanded torque, engine temperature, air charge, etc. maybe determined. At 704, routine 700 may determine if the HPP (e.g., DIfuel pump 228) can be operated in the default pressure mode. The HPP maybe operated in default pressure mode, in one example, if the engine isidling. In another example, the HPP may function in default pressuremode if the vehicle is decelerating. If it is determined that the DIfuel pump can be operated in default pressure mode, routine 700progresses to 720 to deactivate and de-energize the solenoid activatedcheck valve (such as SACV 312 of DI pump 228). To elaborate, thesolenoid within the SACV may be de-energized and the SACV may functionin a pass-through state at 722 such that fuel may flow through the SACVboth upstream from and downstream of SACV. Herein, as explained earlier,a default pressure of DI fuel pump 228 may be achieved by accumulator330. Routine 700 may then end.

If, however, it is determined at 704 that the HPP may not be operated indefault pressure mode, routine 700 continues to 706 to operate the HPPin variable pressure mode. The variable pressure mode of HPP operationmay be used during non-idling conditions, in one example. In anotherexample, the variable pressure mode may be used when torque demand isgreater, such as during acceleration of a vehicle. As mentioned earlier,variable pressure mode may include controlling HPP operationelectronically by actuating and energizing the solenoid activated checkvalve, and regulating fuel pressure (and volume) via the solenoidactivate check valve.

Next, at 708, routine 700 may determine if current torque demand (andfuel demand) includes a demand for full pump strokes. Full pump strokesmay include operating the DI fuel pump at 100% duty cycle wherein asubstantially large portion of fuel is delivered to the DI fuel rail. Anexample 100% duty cycle operation of the DI pump may include deliveringsubstantially 100% of the DI fuel pump volume to the DI fuel rail.

If it is confirmed that full pump strokes (e.g., 100% duty cycle) aredesired, routine 700 continues to 710, where the SACV may be energizedfor an entire stroke of the pump. As such, the SACV may be energized(and closed to function as a check valve) through an entire compressionstroke. Specifically, at 712, the SACV may be energized and closed at abeginning of a compression stroke. Further, the SACV may be closed atthe beginning of each subsequent compression stroke until pump operationis modified. For example, pump operation may be modified when a reducedpump stroke may be commanded or in another example, pump operation maybe changed to default pressure mode. Routine 700 may then end.

If, on the other hand, it is determined at 708 that full pump strokesare (or 100% duty cycle operation is) not desired, routine 700progresses to 714 to operate the DI pump in a reduced pump stroke or atless than 100% duty cycle. Next, at 716, the controller may energize andclose the SACV at a time between BDC position and TDC position of thepump piston in the compression stroke. For example, the DI pump may beoperated with a 20% duty cycle wherein the SACV is energized to closewhen 80% of the compression stroke is complete so that about 20% volumeof the DI pump is pumped. In another example, the DI pump may beoperated with a 60% duty cycle, wherein the SACV may be closed when 40%of the compression stroke is complete. Herein, 60% of the DI pump volumemay be pumped into the DI fuel rail. Routine 700 may then end. It willbe noted that a controller, such as controller 12, may command routine900 which may be stored in non-transitory memory of the controller.

Turning now to FIG. 8, it depicts routine 800 for illustrating examplefuel flow in a DI fuel pump (such as DI fuel pump 228) during differentmodes of DI fuel pump operation in accordance with the presentdisclosure. Specifically, routine 800 describes example fuel flow in theDI fuel pump during variable pressure mode (with and without full pumpstrokes) and example fuel flow in the DI fuel pump during a defaultpressure mode. It will be noted that the controller (such as controller12) may neither command nor perform routine 800. As such, fuel flow mayoccur due to hardware within the DI fuel pump (e.g. DI fuel pump 228).

At 802, it may be determined if the DI fuel pump is operating in thedefault pressure mode. As described earlier, the default pressure modeoperation of the DI fuel pump includes deactivating and de-energizingthe solenoid activated check valve (SACV) throughout pump operation.Thus, fuel flow may occur to and fro through the SACV (also termed,spill valve), both upstream and downstream of the SACV. If the DI pumpis not operating in the default pressure mode, DI pump may be operatingin the variable pressure mode wherein the SACV may be activated andenergized during at least a portion of the pump stroke.

If it is determined at 802 that the DI pump is not operating in defaultpressure mode, routine 800 continues to 804 to confirm if a 100% dutycycle operation (full pump stroke) of the DI pump has been commanded. Ifyes, routine 800 progresses to 806 wherein a suction stroke in the DIfuel pump is determined. During the suction stroke, as described earlierin reference to FIG. 4, fuel may flow into the compression chamber ofthe DI fuel pump via the SACV 312. SACV 312 may be de-energized to apass-through state, in one example, during the suction stroke. Inanother example, SACV may be energized but may function as a check valveenabling fuel flow into the compression chamber but blocking fueloutflow from the compression chamber through SACV 312. Next, at 808,during a subsequent compression stroke in the DI fuel pump, reflux fuelflow from the compression chamber of the DI fuel pump may not occur. Toelaborate, a full pump stroke may include closing the SACV (byenergizing the SACV) at the beginning of a compression stroke. When theSACV is closed, fuel may not exit the compression chamber through theSACV during the compression stroke and thus, reflux fuel impelled bypiston top 305 may not flow towards the step room via the first fuelconduit. Further, as pressure in the compression chamber increasesduring the compression stroke and exceeds an existing fuel rail pressurein the DI fuel rail, fuel may exit the compression chamber throughoutlet check valve (e.g., outlet check valve 316) towards the DI fuelrail.

On the other hand, if it is determined at 804 that full pump strokeshave not been commanded (e.g., less than 100% duty cycle operation),routine 800 proceeds to 810, wherein fuel flow during a suction strokemay be occurring. As described earlier, in reference to FIG. 4, fuel mayenter the compression chamber of the DI fuel pump via the SACV. Further,as noted at 812, fuel may enter the compression chamber via thede-energized SACV (functioning in the pass-through state). The SACV maybe de-energized since the DI pump is operating with reduced pump strokes(e.g., less than 100% duty cycle). Thus, a fraction of the fuel drawninto the compression chamber, based on the desired duty cycle, may beexpelled out through the SACV in the pass-through state in the followingcompression stroke.

During the intake stroke, specifically for DI fuel pump 228 of FIG. 3,fuel may be drawn from each of accumulator 330 and the lift pump intothe compression chamber 308 of the DI pump. To elaborate, fuel may flowfrom the first variable volume 340 of accumulator 330, via entrance 332,into passage 348 of accumulator 330, and therethrough into fuel supplyline 344 at node 362. Additionally or alternatively, fuel may be drawninto compression chamber 308 from lift pump 208 via inlet 399 of DI fuelpump 228. Fuel drawn in from the accumulator 330 and/or lift pump mayflow through fuel supply line 344, past node 362, through first checkvalve 322, past node 364, and through spill valve 312 into compressionchamber 308 of DI fuel pump 228.

At 814, a compression stroke subsequent to the intake stroke at 810 mayoccur. Further, reflux fuel may flow out of the compression chamberthrough the de-energized SACV. Additional details of the reflux fuelflow will be described in reference to FIG. 9. Reflux fuel flow mayoccur from compression chamber 308 through step room 318 of DI fuel pump228. Further, the reflux fuel may flow from the step room intoaccumulator 330 of DI fuel pump 228. As such, reflux fuel may flow fromthe compression chamber 308 to the accumulator 330 only after flowingthrough step room 318.

Based on the demanded duty cycle, at 816, the SACV may be energized toclose. In particular, the spill valve may be energized to close at apoint between BDC and TDC positions of the pump piston during thecompression stroke. An early closing of the spill valve, relative to theduration of the compression stroke, may be desired for a larger quantityof fuel delivery to the DI fuel rail. A later closing of the spillvalve, relative to the duration of the compression stroke, may result ina smaller volume of fuel being delivered to the DI fuel rail.

At 818, once the SACV is closed, fuel flow through the spill valvetowards the step room is ceased. Fuel remaining in the compressionchamber may now be pressurized and delivered to the DI fuel rail in theremaining compression stroke. Routine 800 may then end.

Returning to 802, if it is determined that the DI pump is operating inthe default pressure mode, routine 800 continues to 820 to confirm iffuel rail pressure (FRP) in the DI fuel rail is less than the defaultpressure of the DI fuel pump. As mentioned earlier, the default pressureof the DI fuel pump may be based on the pressure accumulator, e.g.accumulator 330. If FRP is not lower than default pressure, routine 800progresses to 822, wherein a suction stroke in the DI fuel pump may bebeginning.

Since FRP in the DI fuel rail is higher than the default pressure in theDI fuel pump, reflux fuel from the previous compression stroke may belargely stored in the accumulator. Therefore, the following suctionstroke in the DI fuel pump, at 824, may include drawing fuel principallyfrom the accumulator into the compression chamber via the de-energizedSACV. Thus, fuel may enter the compression chamber primarily fromaccumulator 330. To elaborate, stored fuel in the accumulator 330 mayflow from the first variable volume 340 of accumulator 330, via entrance332, into passage 348 of accumulator 330, and therethrough into fuelsupply line 344 at node 362. Fuel drawn in from the accumulator 330 maythen continue through fuel supply line 344, past node 362, through firstcheck valve 322, past node 364, and through spill valve 312 intocompression chamber 308 of DI fuel pump 228.

At 826, a compression stroke subsequent to the intake stroke at 822 mayoccur. Further, reflux fuel may flow out of the compression chamberthrough the de-energized SACV. Additional details of the reflux fuelflow will be described in reference to FIG. 9. Reflux fuel flow mayoccur from compression chamber 308 through step room 318 of DI fuel pump228. Further, the reflux fuel may flow from the step room intoaccumulator 330 of DI fuel pump 228. As such, reflux fuel may flow tothe accumulator 330 only after flowing through step room 318. At 828,reflux fuel may exit the compression chamber through the spill valveuntil a default pressure is attained in the DI fuel pump.

Since FRP in the DI fuel rail is higher than the default pressure in thepump, at 830, there may be no fuel delivery to the high pressure fuelrail. Thus, a significant portion of the fuel situated within thecompression chamber at the beginning of the compression stroke may beshifted for storage in the accumulator during the compression stroke.This stored fuel may be drawn into the compression chamber in thesubsequent intake stroke of the DI fuel pump. Routine 800 may then end.

Returning to 820, if it is determined that the FRP in the DI fuel railis lower than the default pressure, routine 800 continues to 832. At832, a suction stroke in the DI fuel pump may be initiated. The suctionstroke at 832 may follow a previous compression stroke wherein aquantity of fuel may have been delivered from the compression chamber tothe DI fuel rail. Thus, in the suction stroke at 832, fuel may flow intothe compression chamber from each of the accumulator and the lift pump.Fuel may be drawn from each of accumulator 330 and the lift pump via thede-energized spill valve, at 834, into the compression chamber 308 ofthe DI pump. As described earlier, fuel may flow from the first variablevolume 340 of accumulator 330, via entrance 332, into passage 348 ofaccumulator 330, and therethrough into fuel supply line 344 at node 362.Stored fuel from accumulator 330 may continue to flow through firstcheck valve 322, past node 364, via SACV 312 into compression chamber308. Additional fuel may be drawn into compression chamber 308 from liftpump 208 via pump inlet 399 of DI fuel pump 228. Fuel drawn in from thelift pump may flow through first section 343 of fuel supply line 344,across third check valve 321, past node 362 into fuel supply line 344and thereon through first check valve 322, past node 364, and throughspill valve 312 into compression chamber 308 of DI fuel pump 228.

At 836, a compression stroke subsequent to the intake stroke at 832 mayoccur. Further, reflux fuel may flow out of the compression chamberthrough the de-energized SACV. Additional details of the reflux fuelflow will be described in reference to FIG. 9. Reflux fuel flow mayoccur from compression chamber 308 through step room 318 of DI fuel pump228. Further, the reflux fuel may flow from the step room intoaccumulator 330 of DI fuel pump 228. At 838, reflux fuel may exit thecompression chamber through the spill valve until a default pressure isattained in the DI fuel pump. Once default pressure is attained in theDI fuel pump, fuel may exit the compression chamber towards the DI fuelrail, at 840. Since FRP in the DI fuel rail is lower than the defaultpressure in the DI fuel pump, fuel may be delivered from the compressionchamber via the outlet check valve to the DI fuel rail. Routine 800 maythen end. FIG. 9 depicts an example routine 900 describing fuel flowduring a compression stroke in the DI fuel pump embodiment of FIG. 3,when the spill valve is in the pass-through state. Specifically, refluxfuel flowing out from the compression chamber through the spill valve isdirected towards the step room of the DI pump for cooling. Further, thereflux fuel is returned to the fuel supply line at the accumulator,upstream of the spill valve, only after flowing through the step room.Routine 900 may not be initiated by the controller nor are instructionsfor routine 900 stored in the controller. As such, routine 900 may occurdue to the design of the DI pump system and the hardware includedwithin.

A compression stroke in the DI fuel pump may be initiated wherein refluxfuel flow may occur from the compression chamber through the spill valveduring default pressure mode of operation and during a lower than 100%duty cycle operation of the DI fuel pump. At 904, as the pump pistonbegins the compression stroke and moves towards TDC position, the pumppiston forces fuel from within the compression chamber towards the spillvalve (also termed, solenoid activated check valve). Since the spillvalve is de-energized and in the pass-through state, fuel exits thecompression chamber (as reflux fuel).

At 906, the spill valve may be open at the beginning of the compressionstroke in the variable pressure mode when the DI pump is operating withreduced pump strokes (e.g. less than 100% duty cycle). As fuel exits thecompression chamber through the spill valve, at 908, fuel flow isdirected towards the step room. As described earlier in reference toFIGS. 3 and 5, first check valve 322 obstructs reverse fuel flow fromSACV 312 towards accumulator 330 (or LPP 208). Therefore, reflux fuelflow is directed through the first fuel conduit 376 towards the steproom 318. At 910, fuel exiting the spill valve (e.g., SACV 312) may bedrawn into the first fuel conduit via the first end of the first fuelconduit (e.g., first end 372 of first fuel conduit 376). As describedearlier in reference to FIG. 3, the first end 372 of the first fuelconduit may be fluidically coupled to the fuel supply line 344 at node364 between first check valve 322 and spill valve 312.

Next at 912, reflux fuel may flow within the first fuel conduit throughsecond check valve (e.g., second check valve 324) and enter the inlet(e.g., inlet 352) of step room 318. As such, fuel may flow via thesecond end 374 of the first fuel conduit 376 into step room 318. As thefuel flows through the step room, the heated piston bottom (e.g., 307)may be cooled. Further, the step room 318 may also be cooled reducingvaporization of fuel. At 914, the reflux fuel may exit the step room andmay be conducted to the accumulator 330. Specifically, at 916, refluxfuel may exit step room 318 at its outlet 354. Next at 918, this refluxfuel may enter second fuel conduit 356 via the first end 355 of thesecond fuel conduit 356 and may be returned to the fuel supply line 344at node 362. Further, at 920, reflux fuel may be transferred for storageto accumulator 330 from node 362. To elaborate, the reflux fuel maytravel through second fuel conduit 356, and may exit into fuel supplyline 344 at accumulator 330 (e.g., at node 362 downstream of third checkvalve 321 and upstream of first check valve 322) via the second end 357of the second fuel conduit. Further still, the reflux fuel may then flowvia passage 348 of accumulator 330 and may reside in first variablevolume 340 of accumulator 330 during a remainder of the compressionstroke.

Thus, an example method may comprise, when a solenoid activated checkvalve is in a pass-through state, flowing reflux fuel from a compressionchamber of a direct injection fuel pump via the solenoid activated checkvalve and through a step room into an accumulator, the reflux fuelflowing into the accumulator only after flowing through the step room.

In this manner, an example DI fuel pump may enable circulation of fuelthrough its step room by positively pumping fuel from the compressionchamber of the DI fuel pump to the step room of the DI pump through ade-energized spill valve and via the first fuel conduit. The circulationof fuel through the step room may largely occur during a compressionstroke in the DI fuel pump. Fuel may flow through the step room towardsthe accumulator for storage during a remainder portion of thecompression stroke. The stored fuel may be returned to the compressionchamber in a subsequent intake stroke of the DI fuel pump.

In this way, heating of fuel within a step room in a direct injectionfuel pump may be reduced. By initiating fuel circulation through thestep room using pump strokes in a compression chamber of the directinjection fuel pump, a direct injection fuel pump including a widerpiston stem may be adequately cooled. Accordingly, adverse effects offuel overheating such as fuel vaporization, resulting reducedlubrication, seizing of the pump piston in the bore, etc. may bediminished. Thus, pump performance may be enhanced while extending anoperating life of the direct injection fuel pump.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: during a compressionstroke of a direct injection pump when a spill valve is in apass-through state, circulating a portion of fuel from a compressionchamber of the direct injection pump to a step room of the directinjection pump, the circulating including flowing the portion of fuelthrough the spill valve and drawing the portion of fuel into the steproom from upstream of the spill valve and downstream of an accumulator,the accumulator positioned upstream of the spill valve with a firstcheck valve positioned between the accumulator and the spill valve; andreturning the portion of fuel exiting the step room through a fuelsupply line to the accumulator upstream of the first check valve.
 2. Themethod of claim 1, wherein the drawing of the portion of fuel into thestep room from upstream of the spill valve and downstream of anaccumulator includes drawing the portion of fuel from upstream of thespill valve and downstream of the first check valve.
 3. The method ofclaim 2, wherein the portion of fuel drawn into the step room fromupstream of the spill valve and downstream of the first check valveflows through a second check valve, the second check valve arrangedupstream of the step room.
 4. The method of claim 3, wherein the portionof fuel includes reflux fuel from the compression chamber.
 5. The methodof claim 1, wherein the portion of fuel is substantially stored in theaccumulator during a period of the compression stroke, and wherein theportion of fuel is released during a duration of a suction stroke in thedirect injection pump.
 6. The method of claim 1, wherein the directinjection pump includes a pump piston coupled to a piston stem, thepiston stem having an external diameter that is substantially the sameas an external diameter of the pump piston.
 7. The method of claim 1,wherein the direct injection pump includes a pump piston coupled to apiston stem, the piston stem having an external diameter that issubstantially half of an external diameter of the pump piston.
 8. Amethod, comprising: when a solenoid activated check valve is in apass-through state, flowing reflux fuel from a compression chamber of adirect injection fuel pump via the solenoid activated check valve andthrough a step room into an accumulator, the reflux fuel flowing intothe accumulator only after flowing through the step room, wherein theaccumulator is arranged upstream of each of a first check valve and thesolenoid activated check valve.
 9. The method of claim 8, wherein thereflux fuel flows from the compression chamber via the solenoidactivated check valve into the step room via a second check valve in apassage, an inlet of the passage fluidically coupled between the firstcheck valve and the solenoid activated check valve.
 10. The method ofclaim 8, wherein the flowing of the reflux fuel occurs substantiallyduring a compression stroke in the direct injection fuel pump.
 11. Asystem, comprising: an engine; a lift pump; a direct injection fuel pumpincluding a piston coupled to a piston stem, a compression chamber, astep room, and a cam for driving the piston; a high pressure fuel railfluidically coupled to an outlet of the direct injection fuel pump; asolenoid activated check valve positioned at an inlet of the directinjection fuel pump; a fuel supply line fluidically coupling the liftpump and the solenoid activated check valve; an accumulator positionedupstream of the solenoid activated check valve, the accumulatorfluidically communicating with the fuel supply line; a first check valvecoupled to the fuel supply line between the accumulator and the solenoidactivated check valve; a first fuel conduit including a second checkvalve; a first end of the first fuel conduit fluidically coupled to thefuel supply line between the first check valve and the solenoidactivated check valve; a second end of the first fuel conduitfluidically coupled to an inlet of the step room; a second fuel conduit;a first end of the second fuel conduit fluidically coupled to an outletof the step room; and a second end of the second fuel conduitfluidically coupled to the fuel supply line at the accumulator upstreamof the first check valve and downstream of a third check valve.
 12. Thesystem of claim 11, further comprising a controller having executableinstructions stored in a non-transitory memory for de-energizing thesolenoid activated check valve to function in a pass-through state. 13.The system of claim 12, wherein during a portion of a compression strokein the direct injection fuel pump, reflux fuel from the compressionchamber flows to the step room via the solenoid activated check valve inthe pass-through state, into the first end of the first fuel conduit,through the second check valve, and via the second end of the first fuelconduit into the inlet of the step room.
 14. The system of claim 13,wherein the reflux fuel further streams from the outlet of the step roominto the first end of the second fuel conduit towards the accumulatorand the fuel supply line via the second end of the second fuel conduit.15. The system of claim 14, wherein the solenoid activated check valveis de-energized for an entire pump stroke during a default pressure modeof operation of the direct injection fuel pump.
 16. The system of claim14, wherein the solenoid activated check valve is de-energized for aportion of a pump stroke during a variable pressure mode of operation ofthe direct injection fuel pump.